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When to turn base at towered airport?
When at a towered airport and instructed to make "left pattern for runway 3," am I supposed to wait for the base leg turn until tower clears me for landing?  This seems to be the norm, but I can't find anything in the FAR/AIM to indicate what is acceptable.
Related: I often get confused when in the downwind pattern and I hear something like this: "123X, tower, you are #2 for runway 3, following a Cessna on final."  Does this mean I should turn base and follow the Cessna?
I know the correct answer is to ask ATC to clarify, but it would be ideal if this were spelled out in the AIM.

Added [tag:faa-regulations], as phraseology and terminology used indicates US based question. Phraseology and behavior would differ for [tag:easa-regulations].

Related: What is the correct traffic pattern at a towered airport?

You have a few questions here.

...downwind pattern and I hear something like this: "123X, tower, you are #2 for runway 3, following a Cessna on final."

In this case what you will do is continue your down wind leg while scanning for the Cessna traffic, some towers may ask you to "report traffic in sight" in which case you will say "traffic in sight" when you can see the Cessna. If he is on a long final you can begin turning your base (assuming you are in a similar small plane of a similar speed) when he is on your beam (right off your wing tip). This should provide adequate spacing for you to come in properly. Keep in mind that the tower may also instruct you to do things to keep separation like "123X Extend your down wind 1 mile" etc.

...instructed to make "left pattern for runway 3," am I supposed to wait for the base leg turn until tower clears me for landing?

This depends on where you are coming in from. I have flown into towered airports on the runway heading and simply come into the pattern on final and was cleared to land about a mile from the runway. Other wise I typically report my midfield downwind to the tower "Piper 12345 Reporting Left Midfield Downwind for RW24" then the tower will respond with my landing clearance or instructions to extend. While it is the towers responsibility to clear you for landing and what not, controllers are not perfect, you can continue on towards the runway in your pattern but if you have not been cleared you should go-around or ask for clearance.
The other situation I have been in is a case where the controller deliberately does not clear you but has  you come into the pattern and approach. This occurred while they were waiting for an IRF plan to come through for one of the regional jets waiting for departure. Since they did not know when it would come in I was instructed to continue my pattern and would be cleared on final if they did not need to get the jet out. However I was explicitly told I would be cleared on final so I knew what to listen for.

One minor nitpick: When you're given a traffic point-out by ATC it's good practice to report when you have the traffic in sight, even if they didn't specifically ask you to. Once you have visual contact with the traffic the tower can have you follow them and maintain visual separation - it helps with the controller's workload, and they won't keep calling the traffic for you which reduces frequency congestion.  (Common Sense Exceptions Apply obviously: If the frequency is really busy & you can't get the call in it's usually not critically important.)

Very good point. I may be a little bit biased since the controllers at KPNE are very on top of that since there is a lot of jet traffic as well as GA. They will always request you call traffic in sight. Some times you will get a "You are #2 behind Piper on final now" and that they usually just want a "#2 behind piper on final" read back. But you are absolutely correct.

@Dave: Thanks!  Follow up: If the tower doesn't give me any other instructions except for the "make left pattern for runway 21," I can turn base whenever I like?  Worst case, I'd have to go-around if not given landing clearance?

@David, I would always go around if not given clearance just to be safe. And yes if you are in the pattern you can make your turns as you need at a towered airport. They wont call them out for you unless they say something like " Piper 123X extend your down wind ill call your base" even then I have been in the case where I have had to remind them they extended my downwind. They key is to be on speed so that your extended legs are shorter than if you came in to fast.

As a controller, though at a very sleepy airport:
In the first situation, I do not expect you to delay turning base simply because you do not have a landing clearance. I expect you to fly a normal traffic pattern and maybe prompt me with a "turning base" call if I've forgotten to clear you.
In the second situation I would expect you to continue your downwind without turning base, at least until you have the traffic in sight, because I just told you you're number two behind the guy on final. Once you have the traffic in sight you can turn base and maintain an appropriate distance behind them. BUT this is sloppy controlling, and I would try to make it explicit by saying "extend downwind, traffic a Cessna two-mile final" and then once you report the Cessna in sight come back with "follow the Cessna, base your discretion, cleared to land."

There’s no official rule as to when.  Typically in Cessnas or similar light GA aircraft, I teach to do so when the runway threshold is 45° off your shoulder, as the Airplane Flying Handbook suggests.  I will also teach students to reduce power, begin their descent at ~500 fpm and begin to add flaps abeam the threshold.  This will work out such that you have the threshold 45° Off your shoulder when you are about 200 ft below pattern altitude, so that can provide a good gauge as well.
In regards to the radio call out you mentioned, no, that’s not how that works.  The tower is telling you that you will be #2 to land following traffic and then is pointing out to you the position of that traffic relative to the airport pattern so you can easily locate and acquire it.  You will proceed on course as you are, but accord the landing traffic sufficient spacing so he can land and taxi clear of the runway before you land.

I am Australian, but I can't see why these procedures would differ greatly between our countries.
The answer to your first question is no. In the absence of airport-specific published procedures, you do not need to wait for tower clearance to turn base, however you must tell them that you are commencing the turn. Usually once you tell them that you're turning base you are given a landing clearance. The exception is when you are specifically asked to report before turning base - it is not uncommon for tower to ask you to report when ready for the base leg, in which case you must not turn until cleared.
Regarding your second point, if I take it exactly as you have presented it here that is a traffic information message only, with no clearance. The same procedures as above apply. However if you are told that you're following traffic in the pattern, you must not turn base unless you have identified the other aircraft. Accidents have been caused by the trailing aircraft 'cutting in front of' the aircraft in front.

it is not uncommon for tower to ask you to report when ready for the base leg, in which case you must not turn until cleared.- This is why I did not answer, being an EASA-kid. Unless the instruction extend downwind is used, I am free to turn base whenever I like. report downwind is an instruction to report, not to extend.

@SentryRaven That's the common usage in the US too: "Report" means "Tell me", though it's implied that you may be asked to change your plans when you report. (When the tower wants you to do something nonstandard they'll tell you: extend downwind or I'll call your base get used frequently if the tower wants you on the downwind longer than a "normal" pattern would dictate, otherwise you fly a standard traffic pattern just like you would at an untowered field).


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What climb rates can the Airbus A320-200 achieve and which climb rates are commonly used for normal flight operations?
In relation to AirAsia flight QZ8501 officials have been quoted as saying:

"It is not normal to climb like that. It's very rare for commercial planes, which normally climb just 1,000 to 2,000 feet per minute. It [climbing at 6,000 ft per minute] can only be done by a fighter jet."

Two parts of that statement struck me:

The rate of 1,000 to 2,000 feet per minute is stated as "normal", not "maximum"
The claim that only fighter jets can climb at 6,000 feet per minute.

My question is then:

What is the maximum climb rate that an AirBus A320-200 such as the one involved in this incident could achieve with out stalling? (Including configurations and operations outside of "normal")
If it is less than 6,000 feet per minute on the A320-200 can any commercial passenger carrying aircraft in operation today exceed 6,000 feet per minute? (I'd assume Concorde could, but that's no longer in operation)

Was the high climb rate the result of pilot control input, or just a violent updraft?

@User58220 Impossible to answer until the FDR data is released and the investigation concluded.

There's a lot of nonsense being banded about regarding this flight.
First up, we are not talking about sustained, powered climb rates. If you're travelling at Mach 0.85 and pull up vertically, in theory (if your plane didn't break) you'd climb at an initial rate of nearly Mach 0.85 (your original speed minus the airspeed loss when pulling up).... That's near enough 57,000 feet/minute.
If you're at high speed and willing to trade speed for altitude, an Airbus A320 is physically capable of climbing at much higher rates than 6000 feet per minute.... At least until it runs out of airspeed.
A fighter is the only aircraft which would be likely to perform a sustained 6000ft/minute climb rate in normal use, but they're also capable of much higher rates of climb.
The maximum rate of climb you'd see in an A320 in normal use is in the 2000 ft/min range, but that's because it's the highest reasonably efficient rate of climb. That's not the maximum the aircraft is capable of under power (which is more in the region of 4000 ft/min), and is absolutely no indication of that maximum unsustained climb rate.
It would eventually stall at any unsustainable rate of climb, but then again, so would any aircraft even at a sustainable rate... Keep climbing and before too long you run out of atmosphere.
Either way, there is nothing to say that climbing above the sustained climb rate for an aircraft is unsafe or, necessarily, unusual. You trade airspeed for altitude, sure, but if you need to be higher at that moment in time, there's plenty of time to accelerate again later.
From Airlines.Net:

The three are roughly the same at 10,000', at about 2500 fpm. (Maybe a bit more for a light A319, and less for a full A321)
Normal climb rates from 10,000' to about 30,000 are as follows:
A319, 3000 fpm to about 1500 at 30,000'
A320, 2200 fpm to about 1000 at 30,000'
A321, 1400 fpm to about 500 at 30,000'

TL;DR - The official is spouting nonsense s/he doesn't understand. A fighter is the only aircraft likely to be able to (or wish to) climb at a 6000 ft/minute SUSTAINED climb rate, but almost any aircraft can climb at that rate for brief durations in a zoom climb - converting airspeed/momentum to altitude

Presumably in sufficiently unusual circumstances you could trade speed for altitude and then deploy flaps/slats to avoid a stall once the speed dropped low enough too.

There are twin-jet airliners (757/767, A330) that can sustain climb rates upwards of 3000 fpm when at light weights, but this is also during the takeoff climb, at much lower altitudes.

They can, but not even close to 6000

Note that these are calm-air climb rates.  If you get yourself stuck in the core of a thunderstorm, you might see 5000 fpm of climb just from an updraft.

@Jon Story -- actually, there are pilots mentioning 4500-5000 fpm climb rates in light (no pax) 757s on climbout...

The 757 is massively overpowered for the airframe though, compared to an A320

@JonStory -- yes.  3000-4000 fpm is a more reasonable upper bound for an A320.

I've flown some business jets which can sustain 6,000 fpm climbs when light, in cold weather, and while relatively low.  Definitely not on a "every day" basis though.

IMHO Weather is main thing to blame
There are many things contribute to an air plane lifting force during a climb;
1) The plane speed
Faster speed higher lifting force.
Remember Winds also makes the plane's speed slower/or faster
2) Air density:
Higher latitude thinner the air : lower lifting force lower
Storm blow such as in a whirlpool can cause low pressure/thin air space: lower lifting force
3) Climb angle:
Stiffer the angle or "more vertical": less lifting force;
Winds may change directions make climb angle virtually- become more vertically : hence less lifting force
So it still a guess, the plane would be ok if it perform the same climbing in normal weather; however in a violent storm, you couldn't tell what would happen.
So it leaves my own question on this matter : If pilot can manually fly the plane, how could he/she trained in such situation ?
Something about me:
I know nothing about airplane neither being pilot, but I know little in physics

Hi, Welcome to Aviation SE! If you have a new question, please ask it was a new question rather than putting it in an answer to another question.

As far as wind is concerned, it doesn't really end up affecting climb rates (except for updrafts, downdrafts, and brief changes due to changing wind speeds.) Aircraft are flown at a given airspeed, not at a given ground speed. Thus, the speed of air over the wings will be the same regardless of whether the aircraft is flying it head wind, tail wind, or no wind. The speed over ground will vary, but this this does not affect the climb rates.

As far as climb angle is concerned, it's a little more complicated than that. Up to the critical angle of attack, increasing the angle of the wings relative to the air flow over the airframe will actually increase the lift produced by the wing. This effect will generally dominate the loss due to the lift force no longer being exactly perpendicular to the ground. In the short term, pitching up can also allow you to trade momentum for altitude, which can temporarily result in very high climb rates until you run out of momentum to trade.

Considering the Vne of an a320 is about mach 0.9, theoretically if you were travelling at Vne and were to pull back in to the vertical and still be pushing mach 0.75 by the time you reached the vertical, a climb rate of 50,000 feet per minute is momentarily possible.

This does not add anything that existing answers don't already cover.

I have tested the maximum sustained climb rates of the AirBus A320-200 in a flight simulator (FlightGear). As others have stated, this is highly dependent on environmental factors, gross weight, weather, etc, so I have tested in the following conditions:

Clear/sunny weather in a core high-pressure region
Aircraft configured for normal mid-range flight
60,000lbs fuel
Speed of 240knts (tested as giving greatest climb rate)
Climbed at the greatest speed whilst maintaining 240knts
Start altitude of 1000ft
Recorded climb rate at 5000ft intervals starting at 5000ft

I tested a theoretical maximum with no passengers/cargo at 413,900lbs gross and also a full consignment at 474,966lbs gross:

Altitude (ft)
Empty (ft/min)
Full (ft/min)

5,000
7,200
5,100

10,000
5,900
4,300

15,000
5,000
3,600

20,000
4,100
2,900

25,000
3,300
2,300

30,000
2,500
1,700

35,000
1,900
1,200

So the max sustained climb rate in a best-case scenario peaked at just over 7,200ft/min, but tails of dramatically as altitude is increased. Clearly that is unrealistic for actual flight, where I wouldn't expect a commercial jet to climb at more than 2000ft/min.

How can you be sure FlightGear is accurately modelling the performance capabilities of a real A320? Also, something is wrong with your weights: 60,000 lbs of fuel is above the capacity of an A320 and 413,900 lbs is way above the MTOW of 172,000 lbs.

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Is wake turbulence dangerous to planes of the same size?
Small planes are vulnerable to wake turbulence from large planes. In this case the private jet got caught in a tip vortex which exceeded it's roll-control and caused it to flip over. Thankfully it was at a high altitude and managed to recover.
But could a jumbo jet's wake be dangerous to another equal-sized jetliner? Could a Cessna Skyhawk endanger another Skyhawk? I would imagine this is the case takeoff and landing where there is less room for error. But at altitude?
Helicopters at low speeds have much worse downwash than equal-weight planes, so stacking two helicopters vertically may be a better example of danger to your peers.
Edit: A380 vs A380 shows indeed a significant effect.

Related: Accident and Serious Incident Reports: WAKE, and detailed explanation in ICAO Doc 9426 (page 280, and part II in recent versions).

I have a single character change - turbulance -> turbulence in the title. But I can't change it because I don't have enough reputation to make a single-character change. Somebody who can do that, please do that. Thank you.

Yes, wake turbulence can be dangerous to planes of equal size. Not so much at cruise stage, but during takeoff and landing, yes.
The reason for takeoff, initial climb and landing phase being considerably more dangerous is not so much about the altitude, but because during those phases the airspeed is slower, requiring higher angle of attack to create sufficient lift, thus making the wake vortices considerably more energetic. This is emphasized for takeoff and initial climb due to higher mass of the planes (more fuel).
The most tragic example of danger relating to a heavy classification aircraft  flying through the wake turbulence of another heavy class aircraft is the crash of American Airlines flight 587. Even though the crash basically was caused by improper flying technique, wake turbulence was the factor setting the chain of events in motion. However, as pointed out by Bianfable in his comment, while both A300 and B747 carry the Heavy classification, B747 can be, depending on load, more than twice as heavy as the A300.
During cruise, when a higher airspeeds are involved, the energy of wake vortices is spread over greater distance mitigating the effect on other planes.

While the AAL587 accident was indeed a heavy vs. heavy category match, it should be noted that the 747-400 has more than twice the MTOW of the A300.

That is a good point, A300 is in fact not as comparable to B747 as I originally thought.

So maybe cruise-on-cruise wakes are considered "dangerous" only for large-ish mass ratios. But the more intense slow-speed wakes have been a trigger for a crash at a 2:1 mass ratio. So it's not inconceivable they could pose some sort of hazard at 1:1, especially if the spacing rules were to be ignored.

The danger posed by wake turbulence also varies greatly on the relative angle in which a plane flies through the wake. Perpendicular path will certainly give  a rough ride as strong up and downdrafts follow quickly in succession, but flying straight into wake parallelly can easily flip the smaller plane on its back.

If it helps to tune your intuition, consider this. An aircraft experiences drag because it imparts energy to the atmosphere and does this in three ways. It imparts heat energy to the air in its wake by virtue of friction. It imparts kinetic energy by any shock waves that are produced. It imparts kinetic energy by its trailing vortices. In subsonic flow, except close to Mach one, there are no shocks. The most efficient cruise is achieved when the heat energy and kinetic energy are equal, so roughly one half of the engines power output is being poured into those vortices. So, yes, an encounter with the vortex wake of another aircraft of similar size can be very serious.
A sufficient distance behind the generating aircraft, the vortices do decay. Interestingly, they do not lose strength (see the contrails persist for miles!), but that energy is spread out over an increasing diameter.

Nice point of view. "Interestingly, they do not lose strength but that energy is spread out over an increasing diameter" they eventually change into heat due to friction

Contrails are not the same phenomenon as wake votices, one cannot draw parallels between those two. The vortices eventually turning into heat is a good description thought.

@Jpe61 Contrails ARE wake vortices. And to be sure everything eventually turns into heat. That is why contrails eventually disappear.

Nope @PhilipRoe contrails are water vapor from engines. Look it up. Contrails can last for days. Wake vortices do effect contrails, your might be thinking of that?

Why is that water vapor where it is??

@PhilipRoe the engines. They burn kerosene (a hydrocabon), and the exhaust is mostly nitrogen (which is not effected by burning), water vapor and carbon dioxide. Higher up in the atmosphere the conditions are such that water vapor condenses into a visible contrail, regardless of wake turbulence. The wake turbulence then usually catches the contrail, "twisting" it. There are very handsome pics of this around the internet.

The wake has two roughly equal components. Heat due to friction and kinetic energy due to induced vorticity. The vorticity rolls up at about 70% semispan. Centrifugal effects lower the pressure in the vortex cores and thermodynamics lowers the core temperature. Water vapor in the exhaust entrains into the cores and condenses. After that both the vorticity and the vapor diffuse but the diffusion coefficients are comparable. The  OP had doubts whether a large plane would be at hazard from another large plane. My answer conveyed that the energy level is enough and persists for long enough

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Sluggish response to transients in very high L/D ratio airfoils
A sailplane has very high aspect-ratio wings and can have a glide ratio up to 70:1 (the wing L/D ratio is even higher since the fuselage adds drag).
The flow at such high L/D ratios for such long, thin wings approximates 2D potential flow.
Potential flow is how an idealized zero-viscosity incompressible fluid flows. There is no energy dissipation and zero drag. The flow-field has no curl (shear stress is needed to rotate a fluid parcel, which requires viscous shearing on said parcel) and no divergence. This greatly simplifies fluid dynamics calculations and is useful as a conceptual first approximation.
In 2D potential flow lift is proportional to the circulation around the object and the airspeed of the object. Circulation can be thought of as the total amount of curl in a region: the curl in some sense is "concentrated" at boundary of the air foil. Since the vector field is curl-free everywhere else, any curve drawn that goes around the airfoil will have the same circulation.
Any value of circulation can be plugged into the potential flow equations; it is a free parameter. In real life however, viscosity  is used to generate circulation. The most obvious way is to drag air around a spinning cylinder. Since potential flow ignores viscosity, it cannot differentiate between a non-spinning cylinder and a spinning one. But real fluids can.
Airfoils also generate circulation. Trailing edges of airfoils generally point downward with respect to the air-stream, even at zero angle of attack (due to camber). Suppose a glider with very long wings is in still air and is suddenly launched. The flow around the wings initially has zero circulation. But (I think) this is (very roughly!) what will happen: drag from the airfoil will tend to slow down fluid parcels that pass near it. But the trailing edge is tilted downwards, which means that it is initially sheltered somewhat from the airflow and generates less drag. This asymmetry in drag will induce a circulation that speeds up air passing over the top (and slows down air passing over the bottom). Eventually an equilibrium is reached; the Kutta condition gives a simple way to estimate this equilibrium circulation.
This is my valiant attempt to unify three explanations of lift: Newton's "deflect air down", Bernouli's "moving faster = lower pressure" and "potential circulation but with a little viscosity". But there is little drag to get this process going. Naively, I assume that wing with an L/D ratio of 100 must travel 100 times the it's chord before the lift is "fully" built up. Is this intuition (backed up with crude experiments dragging a flat plate through water at an angle) correct?
A symmetric airfoil at zero angle of attack generates no lift. If my reasoning is correct, coating the top with shark skin to reduce drag should cause such an airfoil to have a positive lift.

Where is the question?  This comes across as a ramble.  SA posts are supposed to contain one clear question.
You may want to Google the 'impulsive start' of an airfoil.

Just a couple of clarification from my side, sorry for being pedantic

Since potential flow ignores viscosity, it cannot differentiate between a non-spinning cylinder and a spinning one.

Potential theory only models the flow around a shape; if you know how the flow around a spinning and a non-spinning cylinder looks like then the potential theory can perfectly differentiate between the two (obviously if viscous effects are negligible). Potential theory doesn't even know the concept of lift and it cannot differentiate between a lifting and a not lifting airfoil, that's why the Kutta condition has to be imposed by adding the condition that just above the trailing edge and just beneath it the speed is the same.

This is my valiant attempt to unify three explanations of lift

There are no three "explanations" of lift rather only one mathematical modelling obtained by applying the conservation of mass, energy and momentum i.e. the Navier-Stokes equations. Conservation of momentum is also known as Newton's second plus third law. Bernoulli equation and potential flow are what you get from the Navier-Stokes equations after the simplification of inviscid and irrotational fluid, so all three explanations really are just the same thing (with increasingly degree of simplifications).

I assume that wing with an L/D ratio of 100 must travel 100 times the it's chord before the lift is "fully" built up

The lift starts immediately to be generated, it doesn't need time or space to develop.

A symmetric airfoil at zero angle of attack generates no lift. If my reasoning is correct, coating the top with shark skin to reduce drag should cause such an airfoil to have a positive lift

Coating only the top with shark skin (or anything interfering with the boundary layer) would for sure energize and thicken the boundary layer, virtually making the shape of the airfoil no more symmetric; this will or will not improve the aerodynamic characteristics according to how exactly the boundary layer is modified: for example at low Reynolds number (where the viscous effect of the boundary layer are predominant) I'd expect a $C_l$ no more symmetrical (i.e. not passing through the 0), a smoother stall at an higher AoA, possibly a lower $C_{l_{max}}$ and a drag reduction at high AoA. This is nothing new and this trick is actually broadly used in model airplanes.


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How can a turbofan's fan generate thrust in cruising flight if air is being slowed down?
High bypass turbofans in airliners generate most of their thrust from their fans, not their "cores". However, at cruise they are actually spilling some air past the intake rather than sucking air in (in contrast a propeller always creates a low pressure "suction" in front of it). Given that the air ingested is being slowed down, how can the fan generate thrust? I assume that the air is forced out the exhaust at an even higher speed than cruise? The exhaust has a smaller area than the intake thus the higher exit speed?

While in cruise, air is actually pushed into the propeller or fan, there is no "sucking in" taking place which would imply a lower pressure at the fan than the surrounding air.
Source: TU Delft lecture handout Vliegtuiggasturbines by C.J. Houtman
Pic above was used earlier in this answer, and shows the fan inlet in cruise (left) and at take-off (right). The in-flowing air has kinetic energy, and slowing it down by expansion in the fan inlet:

increases pressure in front of the fan
allows the fan to add energy to a slower airflow, generating lower compressibility losses.

So the fan adds energy to the incoming airflow, both in the form of increased pressure and increased velocity. Further downstream after the fan, the extra pressure is traded in for a further increase in velocity, until the flow is expanded to the surrounding pressure.

However, at cruise they are actually spilling air past the intake

Not really, air does enter the intake. The front end of the fan nacelle is shaped such that inflow is optimised at cruise.

I assume that the air is forced out the exhaust at an even higher speed than cruise?

Correct, this is what creates thrust.

The exhaust has a smaller area than the intake thus the higher exit speed?

Yes, subsonic airflow accelerates when the stream tube diameter is reduced.

(Please change the figure caption to show that cruise is (a) and take-off is (b)))

Sourcing your images & charts would be appreciated and is expected.

@FreeMan Indeed it is, you’re right. It’s from my treasured university lecture handout “Vliegtuiggasturbines”, decades old and paper format only.

Ah, well then, University, course ID & title, professor and time slot, please! :D

@Freeman yep it’s in the figure reference (press Edit)

Unfortunately, that's only visible to those for whom the image doesn't load (as the alt-text), or to those with screen readers (that will read the alt-text to them), or to those with edit privileges (or think to edit the question and discover it there), so I've updated it a smidge. Hope you don't mind.


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Why is a dedicated compressor more efficient than using bleed air to pressurize the cabin?
Bleed air is air "stolen" from the compressor of the jet engine and has traditionally been used to pressurize the cabin. The alternative is to use a separate compressor just to provide cabin pressure, which is supposed to be more efficient.
Both systems consume energy to compress air. But bleed air uses a compressor that you already have, while the "bleedless" system requires adding an extra compressor which takes up weight and space. It also requires its own air intake (adding drag) and potentially a more powerful APU to supply power to the compressor. Given all this extra hardware, why is a "bleedless" design more efficient per passenger-km?
TLDR answer:
The fundamental physics is the same: Cabin air doesn't "care" if it is compressed by the main compressor or in an electric one; both of which require engine power.
But the engineering is very different:

Only take the amount you need; don't waste excess bleed air (for some reason they can't slow the "bleeding" with a valve?).
Wires weigh a lot less than pneumatic piping.
Bleed air is provided at too high a pressure/temperature (several hundred C), the dedicated compressor may not need to compress the air this much?
Fume events are eliminated.

More detailed answer accepted below.

Bleed air is lost air. The last thing you need on an efficient engine is a leaky compressor.

Aside efficiency considerations, bleed air from the compressor might still contain pollutants from engine that have to be filtered-out and still getting in the cabin in tiny amount. I could clearly smell that in a couple occasions I flew in older jets.

Given all this extra hardware why is a "bleedless" design more efficient per passenger-km?

Flexibility and adaptation
But this can only be understood not focusing on the engines only rather by looking at the big picture. Big picture which, in the case for example of a Boeing 787, consists in a shift from pneumatic system to "a greatly expanded electrical system generating twice as much electricity as previous Boeing airplane models"¹.

In a jetliner, the pneumatic system is used for several purposes but, for the sake of simplicity, let's consider only wing's de-icing and air conditioning.

In a conventional "bleedful" airplane, the pneumatic power is supplied by the engines; the engine is the boss: if the engine is running at its nominal power then also the pneumatic system is outputting its nominal power; if the engine is running at its maximum power then also the pneumatic system is outputting its maximum power. So what happens now if our airplane is smoothly flying at nominal power, in non-icing conditions and half empty? Well, the penumatic system is still outputting its nominal power but since there's no need to de-ice the wing nor to fully condition the air in the cabin, then not all of the air bleeded from the engines is used and it's simply wasted through modulating valves.

In a modern "no-bleed" jetliner, the pneumatic system is supplied by ad-hoc electrical pumps which run according to the pneumatic power needed at that moment. If again our flight takes place in non-icing conditions and with half of the plane empty then these pumps just deliver the requested level of pneumatic power and not the one dictated by the engine: there's no need to heat the wing and the air-conditioning system can be adjusted according to the number of passengers without any waste.

So the shift to a no-bleed system has a positive impact on efficiency due to its flexibility in adjusting its working conditions to the actual needs of the moment and not passively to the needs of the engines.
There's also a weight saving due to the removal of pneumatic ducts, heat exchangers, valves and protection systems. On the B787 for example, the APU doesn't supply compressed air anymore but only electrical energy: the ducts normally connecting the APU with the engines and the air-conditioning system are simply gone. This weight saving is obviously partially offset by the need of bigger and possibly a higher number of electrical generators plus relevant cables and control systems.

¹ source this Boeing pdf.

No wasted air is a big one!

The other answer is on the right track, but doesn't emphasize the real difference (IMO).
Let's say it takes 100 hp (or kW if you prefer) to compress the amount of air you need for a given purpose.  The jet engine already has a very efficient compressor, it would be hard to do better with a separate compressor.  Let's assume it takes the same power to do the job either way.
In a bleedless system, we have a generator connected to the engine that pulls off 100 hp of shaft work and converts it to 100 hp of electricity.  We use that electricity to run a motor to compress the air.  These devices each have an efficiency (power loss), but that isn't the important part.  Fundamentally, that power comes from the turbine, it was extracted from the engine cycle.
In a bleed system, we pull a certain amount of compressed air out of the compressor ($\dot{m}_\mathrm{\,bleed}$).  The compressor runs off of the shaft connected to the turbine, so it still takes 100hp of power from the turbine to compress the air.  Roughly speaking, the power extracted from the engine cycle is the same.
However, in a bleed system, you're also stealing air from the cycle.  Without bleed, that $\dot{m}_\mathrm{\,bleed}$ would continue to the combustor, would be mixed with fuel, burned, and then to the turbine where energy would be extracted (to help turn the compressor and other accessories) and then expanded out the nozzle producing thrust.  I.e. the point of the engine cycle.
The air at the end of the compressor not only took power to reach that state, but it still has an intrinsic value to the engine.  The more air flow through the engine, the more ability it has to produce shaft power and thrust.  When you steal some of that air flow, you're penalizing the cycle.
In effect, bleed air puts two penalties on the engine (power extracted and mass flow stolen from the cycle).  Whereas a bleedless system only puts one penalty on the engine (power extracted).
Most bleed loads do not operate at all times.  You need a lot of bleed air during engine startup, but less at cruise.  Some is a constant load (the bleed air used for turbine cooling) and some turns on and off -- air conditioning, engine start, etc.
An engine designed for a wide range of bleed across a wide range of operating conditions (very little to a great deal of bleed from flight idle to cruise and takeoff power) will have a lot of accommodations in the engine control -- and will fundamentally be a bigger, heavier, less efficient engine.  The bleedless alternative is an engine with a wide range of power takeoff at the wide range of operating conditions (few hp to many hp at all those flight conditions).  This is easier, simpler, and more efficient to achieve.
Bleed air for turbine cooling is a relatively constant load (easier to design for) and also keeps the engine a simple, self-contained unit.  It is safer to  cool an engine with bleed air than to introduce a separate electric compressor to do the job.  However, cabin air isn't the same level of criticality and it is easier to add redundancy outside of the engine to make sure everyone has air to breathe.
The 787's 'more electric architecture' tried to move many systems to electric.  This was accommodated by a large starter-generator attached to the engine.  Instead of using bleed air (first from the APU, but then from the #1 engine) to start the #2 engine, it uses electricity (first from the APU, but then from the #1 engine) to start #2.  This allowed the removal of a huge amount of high pressure pneumatic lines from the tail of the aircraft, out the wings, and to each engine -- and from one engine to the other.  Those ducts were replaced with copper wires.
Engine start is the largest bleed load -- once that was removed (and replaced with sufficient capacity in a starter/generator (one electric machine (read mass) that does two jobs), then it makes sense to try to do other jobs using electricity instead of bleed.
So, while removing bleed air is a good thing for the engine -- this is also a systems wide tradeoff that can't just be considered in the context of cabin air, but also all the other jobs that compressed air (and electricity) do on the airplane.

"100 HP of shaft work and converts it to 100 hp of electricity" more like 95 HP of elec and then 90 HP converted back to work by the moter, which is still pretty good.

@KevinKostlan agreed -- there are efficiencies throughout the chain -- and they are pretty good.  The main thing I wanted to do was to not focus on an argument of .95 vs. .97 and instead bring to light the changes to the engine cycle when you remove air from it.

"In effect, bleed air puts two penalties on the engine (power extracted and mass flow stolen from the cycle)." We pay twice either way: in both cases the engine powers the compressor(s) and misses out on the "hotel air" going to the cabin. In both cases each bit of hotel air requires itself and extra engine air to be compressed. The ordinary bleed-air design is "hiding" the secondary compressor as an over-sizing of the engine compressor.
But your other arguments, as well as the safety of avoiding fume events, seem like good enough reasons.

Using bleed air isn't free. In order to produce the same amount of power as an engine with no bleed air taken out, the engine needs to compress more air. This takes energy, and means more fuel used for the same amount of power output.
The extra compressor takes up weight and space. But so does all the ducting that moving bleed air around requires, and the intercooler needed to bring it to an appropriate cabin temperature.
Apparently, in at least some airframes, removing the bleed air system is enough of a gain that even after adding a dedicated compressor and air intake there is still an overall gain in efficiency.

It isn't free either way, but maybe the dedicated compressor is more efficient?

@KevinKostlan My guess is that the bulk of the savings is in removing the extensive ducting required to move the bleed air all through the aircraft.

Another point about removing the ducting: you remove a few severe failure modes. The bleed air typically comes out at around 300~400 deg C, which is hot enough to change the mechanical properties of structural components if a leak happens to hit the structure. Thus, any large aircraft contains several temperature sensors to detect these leaks (and command a bleed shut-off valve) and some diverters, to protect primary structure in case of a leak (these are specially difficult to integrate in the pylons). That adds to the overall weight of the bleed system.


text:
How can I find information about the aircraft with registration / tail-number N58644?
I am trying to find information on aircraft N58644 which doesn't show on the N number listing. This is a BT-13A converted to civilian use from the 40s or 50s. Any ideas where I can get any information since the FAA doesn't show it?

I guess it means that it's not a valid registration, FAA.gov says it's not assigned/reserved or it just got assigned

Can you give some more details about where you've seen or read about that N number? It doesn't show up on this site either, for example.

Even if it were a total loss, the plane should still be listed in the FAA registry...  You could also try contacting the NTSB if you are sure that is the tail number.  Perhaps it was in an accident but somehow it wasn't logged in the FAA database...  You wouldn't be able to search that online because they only go back to the mid 90's.  But you can contact the main office.

I have checked the 01 July 1965 FAA register, and it does not show there. My father had a BT-13A N61907, and it doesn't show either. The usual fate of postwar BT's was sale to crop duster companies; they were of value only for their R-985 engines and 2D30 props to be fitted on Stearman dusters or airshow planes. The airframes were scrapped.
If you can convince someone at FAA OKC, they could call up their archives (in Ft. Worth IIRC) and get the answer you seek.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What lead time is required to change an already submitted flight plan?
A government agency of an EU country commissions a private company with a chartered flight from Europe to Africa/Asia/... (e.g. to involuntarily take people to a specific country).
Then it wants to change the time of departure with short notice. How long before the changed departure time do they need to file the new flight plan and what are some obstacles for changing it at the last minute?

Flight plans change all the time for a wide variety of reasons, up to and sometimes including the moment when the wheels leave the ground. Perhaps you could clarify your question? Certainly the pilot and operations manager at the charter company already know what to do in any specific situation.

I've read some anecdotal evidence that getting the entry permit is sometimes serious problem. Especially in Africa some coutries take it very seriously and at the same time it is a slow bureaucratic process.

@GregHewgill it sounds to me like the OP is an anti-deportation activist that wants to be around when some deportation is to happen and now asks himself whether he needs to camp at the airport or if it is enough to have a look at the flight plan every once in a while.

And this very situation occured between South Africa and Madagascar early in the morning of 13th of October. A former and exiled president were ferried back to his country without the current government knowing him arriving (or they said...) Highly sensible subjects in some countries.

I think if you want an answer to this question you need to clarify if your question is about the general rules for flight plans on international flights, or the specific case of extraordinary rendition flights. The first has an answer, the second one doesn't (because an illegal government-sponsored operation will probably ignore all the rules and do whatever they want anyway)

The flight plan can be changed by the minute, as long as the two governments and the two airports and the airline agree on this.
As it seems like the government pays the airline to just take off whenever they are allowed to, take the airline out of the equation.
Likewise for the airports, since they are either state-operated or have a concession which states that they have to assist in lawful deportations, emergencies or state affairs.
This keeps two governments in, which have to agree on a time and the who-pays-whom-how-much for the deportation to really take place. In fact, I think this is the only reason why the plane is not yet airborne - because of two governments playing their diplomacy games.

The airline still has to fly by the rules, so you can't take the airline out of the equation. For example duty time regulations will apply.

@DeltaLima When the government pays an airline to be ready on short notice at any time (and not just in a small-enough time frame), they pay a premium for either pilots sleeping 24/7 in the airport hotel (if available), two sets of pilots or a spare pilot. The airline has a contract to fulfil, which's contents are unbeknownst to us. This contract takes them out of the equation.

You say the contents of the contract are unknown, yet you state that the contract takes the airline out of the equation. There is no mention of the type of contract anywhere in the question so you are making a lot of assumptions here.

I am the US, but here you can amend a flight plan while in air.  I have done this several times to change the destination from airport X to airport Y.  ATC nicely updated my clearance to the new destination.

The question is about EU countries


text:
What emergency situation can pilots encounter in gliders/non-powered aircraft?
Pilots have to be able to handle a wide range of emergencies in the air. For powered aircraft, the obvious example to me is recovering from an engine failure, but obviously this can't happen on an unpowered glider. Many gliders have no electrical systems, so an electrical failure can't happen. A stall, I believe, can, and I assume the recovery would be similar to in a powered aircraft. What other emergencies should a glider pilot be able to handle? I'm especially interested in any emergencies that powered aircraft don't have to deal with.

I imagine a glider could have every emergency a powered aircraft could have, with the exception of an engine failure or fuel exhaustion situation: You could still have an electrical fire/smoke condition, stall/spin, inadvertently fly into IMC, etc.) You could also fail to find enough lift and have to land somewhere that's not an airport, which is kind of like fuel exhaustion, but that may not quite rise to the definition of an "emergency".

most gliders don't have electrical systems. maybe your iPhone battery can catch fire.

@rbp true, but it's also fair to say most gliders also don't have engines and fuel tanks except the ones that do :-)

interestingly, you don't needs ASEL to fly a powered glider, even one as fancy as an S-10VT:  http://www.stemme.info/aircraft/peak-performer/. but you do need an self-launch endorsement http://www.faa.gov/documentLibrary/media/Advisory_Circular/ac61-94.pdf

"I'm especially interested in any emergencies that powered aircraft don't have to deal with".  Powered aircraft can become gliders (intentionally or accidentally).

@rbp, do gliders not generally even have radios?

Not required (even in airplanes) in class G and E below 10k. Some have handhelds. Some have real electrical systems if they want to fly in B C or D, or even A (yes you can!)

It is not true that most gliders to not have electrical systems.  Almost all gliders do... certainly all gliders you are likely to encounter other than one you built yourself.    However, no critical systems depend on electrical systems in a glider.  But fire is possible.

The number one emergency in a glider is a tow rope break at low altitude, less than 200 feet above the ground with no appreciable headwind. Below 200 feet, the proper technique is to land straight ahead, which usually means landing off airport.
Between 200ft and 500ft, it is possible to make a U-turn back to the runway, and land in the opposite direction in which you took off.  The main hazard with this kind of landing is landing with a tailwind, and once the wheel touches the ground, the flight controls operate in the reverse direction.
Above 500 feet, it is possible to fly an abbreviated pattern and land on the runway you took off from.
Add 50 feet of altitude for each 10 knots of headwind.
Some other tow emergencies are inability to release to tow rope, in which case the tow pilot needs to release the rope on his end; engine failure of the tow-plane; and a double tow rope release failure, which means the glider needs physically break the tow rope (it has a pre-determined breaking strength of 80-200% of the weight of the glider) or to land behind the tow-plane.
You can also run out of altitude and have to land in a field, which is called an "off airport landing." Someone has to come and get you with a trailer, and you disassemble the glider and drive it away. One hazard is the off airport landing in a field, and the farmer comes out with his shotgun.
Other hazards are flying into the clouds or into severe turbulence, which can happen when the glider pilot is flying "wave," a kind of lift generated by strong winds in proximity to
 mountains.
When thermaling, you are flying very tight steep turns, often with other sailplanes who are also trying to gain altitude. Everyone is supposed to fly the thermal in the same direction, and there is the hazard of colliding with other gliders.
Reference: FAA Glider Flying Handbook - Abnormal and Emergency Procedures

Nice summary; also air-air collisions when thermaling in a gaggle.

Flight controls do NOT operate in the reverse direction when landing with a tailwind.  The relative wind is still from the glider's nose to the glider's tail, but with a tailwind the glider has greater ground speed.  It is only airspeed that counts in the generation of lift and control of the aircraft.

Once the SINGLE wheel touches the ground, right rudder will catch the wind on the right side of the sailplane and attempt to spin the glider counter-/anti-clockwise. both my CFI and DE warned me about it last month when I took my commercial glider checkride, and it happened both times. try it. I've updated the answer to notate that it happens on the ground.

I don't fully get the implication of danger in "tight, steep turns." Are tight steep turns always dangerous, or do they just make flying with a bunch of other aircraft even more dangerous?

two reasons: (1) the tighter the turns, the closer the proximity to other aircraft. it also means that one wing is up in the air, preventing you from seeing an aircraft that maybe hidden by it

What maneuver does the glider use to break the tow rope without causing too much stress on the tow-plane?

its called "slack rope," which is when the glider trades off altitude for airspeed, and reduces the distance to the towplane. when this happens, the rope will get a big bow in it. Under normal circumstances, the pilot can remove the slack by yawing towards the bow, allowing the slack to come out gently. To break the rope, the pilot yaws towards the slack, then when the slack almost is almost out, he yaws further away, breaking the rope.

I should also mention that some glider owners have their own tow ropes based in the glider's weight.

Rope related failures (release etc.) can also happen when the rope is operated from the ground (towed by car, winch etc.)

Is the single wheel aft of the rudder? Otherwise I don't understand the explanation of "reverse controls".

The single wheel is under the cabin. Gliders (and airplanes and helis and boats) tend to turn into the wind. All that has to happen is that the wind catches on one side of the fuselage or the other. When the rudder is deflected, say, right, the wind will catch it and want to turn the plane leftward/CCW into the wind, opposite the direction the pilot expects.

@HenningMakholm: Gliders in flight are already super slow. It is possible that while landing with a tailwind the glider would stop aerodynamically (with respect to the wind) long before it stops geographically (losing all its momentum). In which case, halfway down the landing strip it is possible for the direction of the wind to turn 180 degrees and come from behind instead of from the nose.

In addition to the emergencies mentioned by rbp, there's also spin recovery.   Presumably power pilots need to know this as well, but it is more relevant to glider pilots because thermalling can take you close to the incipient spin territory.   In Australia, at least, real spin recovery is practiced until the pilot is proficient at recovery.

Although I did do spin training during my glider, training it's not part of the private or commercial PTS in the USA. It is  however in the CFI-G PTS

Yeah, I recall my instructor mentioned it was not routinely taught in the US, abd how odd that is....

Did you have to initiate the spin? It's pretty hard to even stall some glider trainers. They just mish, unless you're really crisp

Yes,  you learn initiation and recovery.  The Australian training fleet had many glider that are spin friendly,  though a few need canards fitted to make them enter reliably.

The purpose of spin training is symptom recognition to prevent dangerous inadvertent spins in low-altitude high-workload situations where recovery from a full spin may not be possible. The otherwise counterintuitive inputs to recover from an unintentional spin are not unique to gliding.

Another very important accident that can occur is what I know as the Kavalierstart.
It occurs on winch launches with some airplanes when the pilot is not giving enough nose down command during the first couple of seconds.
The airplane gaining speed really fast will pitch up and as it is going up with a very steep angle, the lift will actually pull in the opposite direction of where the winch rope is coming from. Due to the excessive load the rope will break, and as the hook with which the rope is attached to the glider is before the center of gravity, the missing force of the rope will cause the glider to continue pitching up bringing it into extreme nose up or even upside down attitude (as it is already flying up pretty much vertically). Without the rope pulling the glider it will almost immediately lose its airspeed and drop down.
There is no way over recovering this and it usually ends up in killing everyone on board.

Answering an old question but there are issues with the winch launch that have not been covered; one is a wing drop on the ground run. If the wing touches the ground while being winched then the glider can cartwheel if the pilot is not quick enough or able to pull the cable release. The winch can keep pulling the aircraft until the winch operator spots a problem and stops the launch or the pilot pulls the release.
This happened at my club about 3 years ago (2012) with an experienced pilot in a Nimbus 3. He died of his injuries.
There is also the possible issue with cable fouling, although unlikely it is possible in a shallow fast climb to dip the nose on release and impact the cable if the cable parachute has opened. That will ruin your day.
Pulling too far back on the stick on the ground run can cause an overly-quick rotation into a steep climb causing the tail to hit the ground. While removal of the tail will reduce drag considerably it will cause one of two control issues.
In winch launches you are very much at the mercy of your ground crew and winch driver. All it takes is for a misheard instruction or someone to mistake the glider model and you could be launched on the wrong winch setting. An underpowered or overpowered launch can cause a lot of problems for a pilot but then that is why we drill for problems. I have to admit to signalling a launch for the wrong type of glider, thankfully it was spotted by the pilot who radioed a correction but I have seen gliders launched on the incorrect winch setting on a few occasions.
Pilots of Petrol Pigeons don't have a cable to worry about.

Most gliders do have battery and/or solar-powered avionics and comms, so there can be electrical failures. In fact, one must take battery life into account for long flights.
Gliders often fly much higher than other general aviation aircraft, so failure of the oxygen system with attendant hypoxia is a risk.

You should answer once, and put all your answers in the same answer

Let me add some more possible failures:

Incorrectly assembled aeroplane ( actual reason for some tragic deaths ). Avoided by following check lists and instructions before even contemplating to start.
Items dropped in the cockpit may lock up controls ( I did drop a water bottle down among the cables, luckily not locking up the controls )
In air collision, especially when flying in clouds ( One reason flying in clouds generally not allowed in competitions )
Heat stroke: the cockpit has plexi glass all around and in sunny weather it will be very warm. Never forget you most important personal safety item, the hat.
Out of oxygen: we from the "low lands" can not stand any long time up high. Once above 10.000 feet (3.000 meters) we should have Oxygen along. Note that in wave flying a glider might reach 10.000 meters.
Out of energy, already mentioned in other answers. Pilots train for this and are supposed to commit to landing once reaching minimum height above ground. Add a bit to the minimum when over rocky terrain or over dense woods.


text:
How do you properly enter the NDB34 published approach at Friday Harbor (KFHR)?
I'm having trouble figuring out the correct procedure to enter an approach such as:

Let's say you are cleared from ISLND for the NDB approach.  How do you maneuver safely and legally to the the outbound leg once you reach the IAF?
My guess is the correct way would be a turn to the outbound course from the NDB.  Then a right turn direct to the NDB and a direct entry to the outbound course, then proceed as charted.

Even better:  how would you approach from WATTR?

This chart is starting to make no sense honestly.  I would say that from WATTR that NOPT should be indicated

@John Remember, WATTR and ISLND are not IAF's, so think of this the same way as being cleared direct to Friday Harbor NDB for the approach, from wherever you happen to be.  FHR is the IAF....

Right.  That makes sense.  It can't be NOPT since you have no way of knowing your distance from FHR.  You need to get to FHR first to ensure you stay int the safe area.

First of all, do not let the depicted holding pattern confuse you.  It is only there because the missed approach procedure happens to have the hold at the same place, and for the purposes of the course reversal may be ignored.
In this case, you have options because the course reversal is simply a "barbed arrow".
AIM 5-4-9. Procedure Turn and Hold-in-lieu of Procedure Turn(a)(1) says:

On U.S. Government charts, a barbed arrow indicates the maneuvering
side of the outbound course on which the procedure turn is made.
Headings are provided for course reversal using the 45 degree type
procedure turn. However, the point at which the turn may be commenced
and the type and rate of turn is left to the discretion of the pilot
(limited by the charted remain within xx NM distance). Some of the
options are the 45 degree procedure turn, the racetrack pattern, the
teardrop procedure turn, or the 80 degree 260 degree course
reversal. Racetrack entries should be conducted on the maneuvering
side where the majority of protected airspace resides. If an entry
places the pilot on the non-maneuvering side of the PT, correction to
intercept the outbound course ensures remaining within protected
airspace. Some procedure turns are specified by procedural track.
These turns must be flown exactly as depicted.

In other words, do what you want as long as you either stay on the protected side or correct to intercept the outbound course if you find yourself on the non-maneuvering side and you stay within 10 miles of the NDB.
Personally, I would:

Cross the NDB and then simultaneously:

Turn left to a heading of about 129 degrees (depending on the wind)
Descend to 2,300 feet

Start the outbound timing as I cross the 69 degree bearing TO the NDB (90 degrees)
Intercept the outbound course of the procedure turn and then fly the rest of the course reversal as depicted (the 45 degree procedure turn).

However, as I said in the beginning, you can do it however you like within the constraints that the AIM gives.
I did find a rather interesting article which states that ICAO rules are a little different, but I won't go into the specifics since this is an FAA chart.  For those who are curious though, take a look at it here:  Course Reversals.

This. I've flown this approach and what is described works just fine, thank you very much.

Wouldn't a right turn be more suitable for this chart? Considering the two obstacles and the Canadian border on the west side of the approach. Also, if you cross the NDB then turn left to 189, wouldn't you'd be headed SW, away from the approach course?

@kevin Correct on the second part, it should have said 129 (that's what I get for writing the answer late at night on my phone, lol), I've updated the answer, thanks.  As far as the first part, the approach was designed with those obstacles in mind, and is the reason that you can't descend until you are established on the outbound course.  Your certainly could make a right turn, but it would be the long way around and there is no reason to do so.

Since the NDB is the only navigational reference, you don't have much choice but to fly right over it.
So, ISLND direct FHR, turn right and intercept 159 FROM, as indicated. Once you're established on the 159 FROM, do the procedure turn exactly as shown, and stay within 10NM of the NDB.
Notice all maneuvering is to the east of FHR, that's the "safe area," since there are two obstacles on the west side @424ft and 1100ft, as well as the Canadian border.

How would you turn right and intercept 159.  Are you suggesting the correct approach would be something like go direct FHR then right turn (294 degree right turn).  I would imagine that at a minimum you'd need to do something of a tear drop (similar to the depicted missed approach).  Meaning direct FHR, 339 FROM then right turn direct FHR, left turn 159 FROM.

From ISLND, fly the ADF inbound on whatever bearing keeps the need from moving. when the needle flips around, you've reached the NDB, so set the ADF to 339 (159 + 180) TO. Initiate a right-hand turn until the needle reads 159 TO, and intercept.

Joe pilot answer was not totaly correct.
I'll try to explain in a more easy way.
You are on ISLND in a Direct heading (273° for 14.5nm) for FHR NDB.
When you are over FHR NDB, start your left turn to intercept the RAD 159° FROM FHR, and begin descent 2300ft
At 10nm, you need to turn left heading 114° after 1min or 2min  right turn to HDG 294° and intercept RAD 339° TO FHR, when you are on RAD 339° TO FHR, i wish you a great approach and an Happy Landing !
I think, Dotted line was used for Go Around Procedure.
(Sorry if my english is not perfect)

Edit : A friend gived to me a Jeppesen Chart of KFHR (maybe outdated, but very close to your chart), but i only display a little part of the chart

You don't have anyway to know when you are very close to FHR (since you likely wouldn't be flying this approach at all if you had a GPS).

With an ADF you won't know your relative distance to the NDB.  You'll only know when you pass it

Alright, sorry i was disturbed because i have some many exemple with DME... =(, but you know the distance, and you have capability to determinate after how many time you can begin your turn if you don't want to overshoot FHR...

you're treating this like a VOR, not an NDB. there are no Radials, only bearings.  Its wrong


text:
Why does the airport plate list a VASI that does not exist?
I have a small but quite busy GA (General Aviation) airport I operate out of that gets over 140,000 of operations per year.  It's a popular GA destination, has an active school, and the area schools use it as a great short, narrow, practice runway. The AFD (Airport/Facility Directory) entry for the airport lists the runway as having a Tri Color VASI (Visual Approach Slope Indicator) at each end.  It doesn't exist.  As far as I've gathered it might have existed 20 years ago.
How does an oversight like this exist for such an extended period of time?
Is this something that should be reported?
The instrument approach plate lists the VASI as well, but it's never been NOTAM'd out of service.  Does this create a hazard to potential IFR traffic?

For more information about correcting the IFR chart, see this question/answer: http://aviation.stackexchange.com/q/320/69

Harvey Field (S43)?

How does an oversight like this exist for such an extended period of time?

Because it doesn't get reported.

Is this something that should be reported?

Yes, it should be reported, otherwise this oversight will exist for an extended period of time.
This dAFD website contains a link that should be followed to [r]eport any A/FD errors or changes. Somewhere down those links you'll find plethora of forms and rather confusing texts which seem not really helpful when you want to report a missing VASI. That brings us back to the answer on your first question.

Update:
In the comments, Kevin Cathcart pointed out the Aeronautical Data Inquiries form which is the appropriate form to flag the problem. Alternatively you can contact the NFDC (National Flight Data Center) via phone at 1-(866) 295-8236.

Does this create a hazard to potential IFR traffic?

Whether it is a potential hazard depends mainly on the presence of other source of vertical guidance. Is there an ILS / gideslope active? No vertical guidance at all is a safety risk in low visibility conditions.

It absolutely could be a hazard, I suggest you ask airport management about it and ask them to get it resolved. If they don't, report it yourself. Why should you do their work for them?

Most of this confirms what I was thinking. I did my night flights for training there and it was exceptionally scary. I looked into reporting the discrepancy in the AFD, but it looks like the form needs someone from the airport to authorize it. I have in the back if my head a suspicion that they have an interest in keeping their imaginary VASI.

@John, that is what I found as well. Getting someone to authorize it seems an unnecessary high barrier to report an error in the A/FD. To really change the A/FD I think it is fair to require authorization, but just flagging a problem should be made easier. If you look into the question / answer linked from  Lnafziger's comment you'll find an email address and phone number that might be of help. If you think this is a safety issue you should consider reporting it though http://asrs.arc.nasa.gov. You are definitely not the only one reporting missing/inoperative VASI's.

For flagging the problem the appropriate form would be the Aeronautical Data Inquiries form. That form exists for "comments" and "questions", which will mostly be reporting apparent problems. If you select airport on that form,   you can enter the airport code, and pick "lighting" (since that is the category name that represents all lighting based visual flight aids). Lastly, you can contact the NFDC via phone at 1-(866) 295-8236. They do need to make it clearer that you should report errors with that form.

They are very good about fixing errors when reported.  As a student pilot, I noticed that the A/FD comments on an airport described "Wildlife in vicinity of Rwy 38".  I called, and it was fixed in the next printing.

Lastly, if you really don't want to deal with the NFDC for some reason, you can also contact the FAA AeroNav division, like you were reporting a chart problem. They state that you can contact them directly about errors in charts and related products, and the A/FD is clearly a related product. They are used to working with NFDC since many chart errors come from errors in the underlying data, and the charts are required to reflect the underlying data, so fixing the error means they need to fix that data.

@KevinCathcart That's excellent information. I've added it to the answer. Of course you could put in an answer yourself and I'll refer to that instead.


text:
Why does the BAe 146 have higher maintenance costs than other comparable jet aircraft?

In many discussion(1)(2) it is stated that the BAe 146 has higher maintenance cost and higher cost of operations in compare to other jets due to its complexity.

Quoting IslandHopperCO (Reply 21): The PSA (then USAir) BAe-146s were
  parked in the desert in 1991 due to high maintenance costs according
  to USAir. More likely was that USAir couldn't turn a profit on the
  western routes that PSA used to make money on, because those routes
  were dropped when the plane were parked.
No that is pretty much correct...PSA also had major problems with
  reliability. In fact BAE provided them with a spare because they broke
  down so much. Who knows if they would have gotten rid of them because
  of that. They were kinda ugly but in a cute way....that smile really
  did it!

Why are the maintenance and operating cost higher?
Why is it more complex than other jets?

The biggest contributing factor is probably having twice the number of engines as other regional jet aircraft.

higher maintenance cost and higher cost of operations in compare to other jets due to its complexity.

That seems ironic considering what Wikipedia says

According to the BAe 146's chief designer, Bob Grigg, from the very start of the design process, making the aircraft as easy to maintain as possible and keeping operator's running costs as low as possible were considerably high priorities.
Velupillai 1981, pp. 1245-1246, 1253.

Why is it more complex than other jets?

Because it has four engines? I believe short-haul airliners of similar capacity mostly have only two.

Why are the maintenance and operating cost higher?

Wikipedia says of the original Lycoming engines used:

The ALF 502 has experienced multiple issues. Its internal electronics could overheat, triggering an automatic shutdown of an engine with no option of in-flight restart, and certain rare atmospheric conditions could cause a loss of engine thrust due to internal icing.[29] Additionally, the BAe 146 experienced aerotoxic syndrome due to leakage of tricresyl phosphate (TCP) into its bleed air; this has been blamed on problems with leaking engine seals. Exposure to these toxic fumes is a dangerous health risk

Note: the above is speculation, you'd have to ask an airline maintenance manager.
There are interesting maintenance anecdotes / whinges at pprune

High price of spare parts.
Accessibility of some components.
N1 harness that goes through engine fan strut.
Quick release fastners needed on engine core covers.
FADEC harness (RJ) can't be changed without dropping the donk.
Lower engine power cables that freeze full of moisture.
Corrosion issuse with the gear bay longeron strut.
The nose landing gear steering lube leaks out and the internals corrode
Air con pacs are unreliable.
Honeywell apu's are unreliable, Garrets better.
Fuel tanks need proper draining off every day to get rid of moisture.
Tri-wing fasteners often fail on removal.

The reason is really the number of engines. Engine maintenance is the biggest part of aircraft maintenance, and designers put as few on an airplane as they can get away with. Two is the minimum for redundancy, and any more means more hours have to be spent in the shop. This explains the 777 - it's the biggest thing Boeing could build once the GE-90 was announced.
Why the 146 has four engines is explained in the comment of @fsintegral below, but at least it helped to sell it in some cases. Crossair used them because the owner, Felix Suter, wanted to have his own four-engine transport. The nickname for the 146 at Crossair was Jumbolino.
BAe sold the 146 for very low prices, so the saved money could cover the more expensive maintenance for some years.

I presume the choice of four relatively small engines was down to the design goal of minimising noise while having good STOL performance.

I thought the GE90 was developed specifically in response to the call for engines for the 777 program? In fact, the P&W engine options were the first ones used on 777s. The GE90 wasn't available until a couple of years after the initial launch of the 777. Having said that, the GE90 really is in a class of its own. Nothing else even comes close to the GE90-115b.

@reirab: The first GE-90 777 was delivered in November 1995, half a year after the first 777 was delivered. Engine design takes longer than airplane design, and Boeing needed to be sure that it would have possibilities for stretched versions. The first 777 had an MTOW of below 250 t, the newer versions weigh more than 350 t. Only when engines like the GE-90 were on the horizon, the risk of developing the 777 was manageable - and Boeing wanted to be there first.

@gsnedders: I heard the rumor that the 146 was influenced by the British Air Force who wanted to have a modern close-support transporter. Then four engines would make sense. But in the end the RAF declined the offered militarized version.

@PeterKämpf Ah, you're right about the dates. I had misread them. I saw the 1993 production date for the 777 rather than the mid-'95 first-delivery date.

Thanks for the 2 really Brilliant answers. @Kämpf You think Felix Suter only bought it because of the number of engines? It's a pitty that his "Hello Air" got bust. I'm still angry how the government handled the Swissair debacle.

The BAe 146 was designed to meet the following requirements : Being able to operate on short fields. Quieter than any other model at the time, to be able to operate on city center airports like London City even late in the night. Larger capacity on smaller airfields. Larger models with more payload while still quiet enough (cargo/combi versions already envisionned) => 4 engines was the only option. - At that time, laws on noise abattement wasn't like today and fuel costs wasn't that problematic. Note : The BAe146 is NOT an Avro RJ. The two has different engines, avionics, etc.

the 146 is not an Avro? then which one is a "smurf jet"?

@rbp. I'm assuming both are. Aircraft nicknames pops out soon enough and I highly doubt it took ten years (first BAe146 - first Avro RJ) to give it a nickname. "Smurf jet" refers to its look (stocky) and the 146-100 entered service after the -200, which could have raised more teasings.. I'm just assuming of course. It took a while before "BAe" was refered to "Bring An Engine" though..

BAE according to the accounts of a local Aircraft Engineer stood for "Bring Another Engine".
Engine reliability is was really was the death of this aircraft. At least in my friends experience. Their local examples were constantly having to be taken off line due to hangar time.

Because it was a pain in the a*** to work on. The only benefit the aircraft had was it's ability to operate in noise curfew limited airports (yes, it had an attribute, it was very quiet). Maintenance manhours were very high compared to other aircraft. Engine changes, too many, compared to other aircraft, engine issues, too many, cockpit design, antiquated, spar issues, the list goes on.

Welcome! Unfortunately, this answer is rather vague and doesn't seem to add much to the other answers. It seems almost a given that maintenance costs were higher because maintenance man-hours were higher so the question is essentially why that was true.


text:
Is it a rules violation for a pilot to intentionally frighten a passenger to the point of hysterics?
I saw a "viral video" inside what looks like an inline two-seater being flown from the front seat (shot from the back seat). In the video the pilot slumps over sideways against the window and throttles down, increasingly letting the nose dip, while his passenger freaks out behind him thinking he's passed out and they're going to crash. Eventually the pilot throttles back up and levels off, then turns and smiles at his passenger, having played a trick on him.
The video is almost certainly staged (given how steadily the supposedly-hysterical passenger holds the phone taking the video), but it made me think: Given the unpredictability of people when faced with a life-threatening situation, if it were real, would the pilot in question be breaking a rule and/or law by inciting hysteria in that way? (As opposed to just acting like a massive [expletive deleted].)
Dave, whose eyes are clearly better than mine, says the plane is at about 2,900ft when the pilot starts his little trick and 2,400ft by the end of it, briefly exceeding 1000fpm descent. In addition to my main question, I'm curious whether that's a factor in whether it was a violation; goofing around at low(ish) altitude seems like a Bad Idea™. But the altitude is a side thing (particularly as they were clearly much higher than I originally thought), I'm primarily interested in intentionally inducing hysteria in a passenger.
I suppose we have to choose a locale, so let's say in the U.S.

Do you have a link to the video, its hard to say if anything was out of line without some visual context to this. Also a pitch down and "loses significant altitude" at 500-700ft. will put just about any plane into the ground so something does not add up there.

... not to mention if it was staged there is no chance they staged it that low. Judging altitude is hard, it was probably much higher.

@Dave - I was intentionally avoiding linking to it because I figure it's clickbait, but: https://www.facebook.com/JuskoPinas/videos/3053213521360652/ "Significant" meaning "of what's there." To me, 100ft is a lot more significant at 700ft than at 17,000ft.

@Jamiec - Yeah, I probably have that wrong. Not a trained pilot. (I'm reassured to hear it's hard to judge altitude. :-) ) But for me the altitude is a side issue; I'm curious about inciting hysteria in your passenger.

Obligatory mention of 14 CFR 91.13 - Careless or Reckless Operation

@RonBeyer - Thanks, I figured there had to be some kind of catch-all regulation for that. But aside from goofing around at low altitude, would feigning having passed out to freak out a passenger qualify? (I mean, to me, yes, but I don't know the standards that are applied...)

I don't believe there is a specific rule about "freaking out your passenger". There is the one I mentioned and if the passenger were really upset by it, they could contact the FAA and complain, but it is highly unlikely the pilot would face much more than a "stern talking to" or some retraining. Usually as pilots we don't want to make our passengers uncomfortable, there is a lot of stuff within reach of the passenger in a small aircraft that can make it difficult to fly (like if the passenger grabs the yoke or locks up on the pedals).

@RonBeyer - I don't mean something quite that specific, but maybe something around needlessly creating a hazardous situation. (But then maybe that's nebulous enough it only falls under 14 CFR 91.13.) As you say, in a small craft the passenger can reach things Best Left Alone. :-)

It's not illegal to be a jerk. If it were, we'd run out of prisons long before we ran out of jerks.

@StephenS - No, of course. But creating a potentially hazardous situation when you're pilot in charge is rather more than just behaving like a jerk. :-)

Isn't intentionally, seriously frightening non consenting strangers illegal even on the ground, as harassment, intimidation, arguably assault?

The passenger pulling back on the stick rapidly and stomping on the "brake pedal" at the same time could induce a snap roll instantly. That would completely destroy the non-pilot passenger's psyche enough to lighten the weight of said passenger quite nicely.

https://www.thenational.ae/arts-culture/paris-hilton-to-sue-ramez-in-control-for-plane-prank-1.44018 ... although I don't know how the court trial (if there was any) ended.

@quant - Subsequent reports are that she was in on it from the beginning.

This simply shows that all the viral pranks are stupid fake.

You mean like this?    https://www.pinterest.com/pin/176836722838414875/?lp=true

There's no regulation that I can see that says "don't frighten your passengers". And there probably shouldn't be: almost anything could frighten a nervous person who isn't familiar with aircraft, even if the maneuver (or whatever) is completely normal.
Having said that, if the FAA thinks you've done something stupid then they do have a 'catch-all' regulation that they could argue you violated.
14 CFR 91.13

No person may operate an aircraft in a careless or reckless manner so
  as to endanger the life or property of another

I haven't watched the video but I think it's at least plausible that the FAA could say that there was a real risk that the panicked passenger would take the controls and try to fly the aircraft themselves. In a dive, pulling up suddenly could easily stall the aircraft and stall recovery is not intuitive or obvious to a non-pilot. In the worst case, pulling up suddenly from a dive can actually tear the wings off. So it would be very easy for the passenger to damage or destroy the aircraft and potentially fly into people or property on the ground.
Finally, apart from the aviation regulations, it might be possible for the passenger to sue the pilot for causing stress and emotional damage. You could always ask on law.SE about that.

pulling up suddenly from a dive can actually tear the wings off  I recall on my first flight long ago, somebody tried to assuage my concerns by pointing out that even the most violent turbulence can't cause the wings to come off... and since then it's amazing how many things I have learned actually can tear the wings off!

A comment on the question suggested the possibility of the passenger trying to use the "brake pedal" (actually rudder) at the same time and inducing a snap roll. Other than mechanical damage, could any of this induce a spin or other condition the actual pilot might have trouble recovering from in ~2000ft, after pushing the passenger off the controls? Passenger-induced stall at ~2400ft doesn't seem too dangerous with the pilot actually alive.

@PeterCordes that'd depend heavily on the specific aircraft and possibly atmospheric conditions. Some aircraft are nearly impossible to spin, others spin when you just look at them.

At my flight school there was an event when a glider student almost killed himself and his instructor. In a winch launch, the cable snapped. It's quite a normal event and we are all drilled how to handle it. However, the student was new, and the noise of the cable snapping and the sudden negative G as the instructor put the aircraft from a steep climb into a glide panicked him and he did the newbie mistake when the nose suddenly drops: he grabbed the stick and pulled it with all his force. Thankfully the instructor was physically much stronger and could maintain control against his pull.

"And there probably shouldn't be:" on a recent domestic flight a passenger a few rows back woke up just as we started our takeoff roll and started screaming, apparently terrified the plane was crashing. (He regained his situational awareness and calmed down after a few seconds) So if that was a law you might be bit during a normal takeoff.

@Michael, turbulence, or pulling up suddenly, can't tear the wings off as long as the aircraft is flying below “manoeuvring speed” ($V_A$). Below this speed, the wings will stall before exceeding the design load. Pilots know it, and when turbulence is encountered, will slow down to “weather penetration speed”, which is some margin below this limit, so in normal line flight, turbulence indeed can't destroy the aircraft. But if somebody flies the aircraft too fast, then turbulence, or pulling up too hard, can destroy it.

I'm not sure how much extra force you can apply after a dive, but tearing the wings of a plane off is difficult. I think in a lot of aircraft the fuselage itself is weaker than the wing-fuselage connection. Btw if you stall from pulling up the nose after a violent dive stall recovery is actually "easy": you have the velocity that you don't even need to level the plane to get out of stall. Problematic stalls are due to lack of velocity.

First off, the altimeter is visible at various parts in the video, so we have an idea of exactly what is going on. The aircraft enters the "maneuver" at 2900ft and rolls out of it around 2400ft. Assuming that they are over land nearish to sea level, then they are likely always above the required 2000ft for safe altitude.
Broadly they are in violation of (Ron posted a comment as I'm writing this)

14 CFR § 91.13 - Careless or reckless operation.

But this is the FAA's most broad regulation, and they can chose to apply it how they see fit. In the video, the pilot appears to have full control of the plane, can consistently see forward and does not really maneuver the aircraft in any dangerous way. You can see on the VSI that the descent exceeds 1000 feet per minute at one point, which is fast but not out of the question for a small plane.

My old eyes couldn't make out the altimeter reading. :-) I get that the pilot was always in control. My question is primarily about the inducing hysteria in the passenger.

@T.J.Crowder It's all down to whether it's considered dangerous to have a hysterical passenger. Whether that's the case, is hard to tell. Possibly not even the FAA knows this till they have a case like it.


text:
What's the maximum seat configuration for a 747 that is actually used?
I'm curious what model and configuration of the 747 has the most seating capacity actually used somewhere in the world. The Wikipedia page lists "typical" seating, maxing out at 467 (the 747-8). But that list also shows "Exit limits" on the 747-400 as 550 or 660 depending on exit type, and the 747-400 article claims the 747-400 can be configured in a single-class setup with 660 seats (matching that upper exit limit). The 747 article says:

In Japan, 747s on domestic routes were configured to carry nearly the maximum passenger capacity.

The linked article "isn't available in my region" but a copy viewed via the wayback machine says:

At the opposite end of the luxury spectrum is what All Nippon and Japan Airlines have done to a few of their 747-400s for high-density domestic routes in Japan.
They carry nearly 600 passengers in one class.

So, is the 660-seat 747-400 configuration actually used anywhere? Or if not, what's the largest actually used, and what model is it?

The maximum was likely 568 seats.
It is hard to find a definitive source for this, but it is likely that the 747-400D (Domestic) version had the largest number of seats since it was specifically built for this purpose. This type was used by Japan Airlines (JAL) and All Nippon Airways (ANA). JAL published the number of seats they used in a press release:

How many seats in JAL's passenger 747s: We have many configurations for international and domestic airplanes. The latest international route 747-400 has 348 seats - 12 in First Class, 99 in business class and 237 in economy class.
Our domestic Short Range 747s have as many as 568 seats in two classes: 24 seats in the domestic version of First Class, which we call Super Seat, and 544 seats in regular economy class.

(jal.com)
Here is the seat configuration used by JAL:

(image source: simpleflying.com)
I did not find a statement by ANA itself on their seating. The following article however lists 565 seats as their configuration, so 3 less than JAL:

The Boeing 747 – once dominant in the sky is slowly fading away. The latest airline to wave goodbye to the Boeing  747 is All Nippon Airways, who completed the final flights on its domestic routes.
It marks the end of Boeing 747-400s by a Japanese airline – and also the end of an era of the passenger heavy Boeing 747-400D aircraft.
These aircraft had a massive passenger load of 565 seats on a plane.

(economyclassandbeyond.boardingarea.com)
While not impossible, it is unlikely that another airline would have ever operated a 747 with a higher seating capacity.

That comports well with the quoted article. Thanks for the more precise and better sourced info!

I'm surprised that neither airline went for the full 660 seats...

I dug up old flight schedules I had for ANA from 1997 and 2000 and they also had a 569 at the time, but it was reduced to 565 in the 2013 schedule I have.

In the 1970's and 80's Canadian Airline Wardair flew the 747 in an all economy configuration of 456 seats with a 34 inch seat pitch. And very comfortable it was too.

Hi John. Welcome to the site. We are very focussed on getting actual answers to the question asked. Given that the other answer talks about a 568 seat configuration, this can't be the maximum configuration, which is what the question asked for. Please have a look at our help for more information about how we work.


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Why does the lack of a magneto affect engine RPM?
So I don't have my pilots licence, but I was part of the Australian Air Force Cadets for nearly 8 years (wonderful organisation). During this time I went on a number of flights in Cessna 172's and Cessna 152's. I always noticed that as part of the pre-flight check, the pilot checked both magneto's and this corresponded to a slight RPM drop on the engine.
Why does the lack of a magneto affect engine RPM?

Firstly, to understand the answer, we need to understand that the Cessna 152's and 172's run a 4 Cylinder, Horizontally-opposed Engine. Each Cylinder has 2 spark plugs, one on the top side of the cylinder head, and one on the bottom side. The spark plug ignites the fuel/air mixture that has been sucked into the engine, and causes a controlled burn to push the piston down the cylinder and turn the crankshaft in turn (hence turning the propeller as it is connected to the end of the crankshaft).
Now, as I've stated, each cylinder has two spark plugs, one connected to the "left" magneto, and one connected to the "right". If we turn one magneto "off" (or ground it to be politically correct), only one spark plug in each cylinder will "fire" to ignite the fuel/air mixture. This causes the mixture to have a delayed and less effective burn, meaning that the piston does not get pushed down the cylinder as effectively, meaning the crankshaft will not rotate as fast, and hence, leads to a drop in the Propeller RPM (Revolutions per Minute).
We check the magnetos on the ground to check that:
A. They both work, and the engine won't die if we lose a magneto (we should be able to return to land on the remaining serviceable magneto)
B. We are checking that there is no "Spark Plug Fouling". The fuel we use in aviation contains lead, and hence after a time of running the engine at low power settings on the ground, the lead in the fuel will accumulate on the spark plug head (instead of being burnt off when the engine is working under power), and cause the spark plug to let off a limited spark, or completely block the spark, hence again, making our engine less efficient.

Thats a great answer. I'll leave off marking it as correct (in true StackExchange tradition) for about a day. But great work, that makes a lot of sense.

Glad I could help :) Just out of curiosity, where did you do AAFC?

713 Squadron - Cannington

Excellent answer.  Concise, easy to understand, and accurate.

I would also add that, C. it checks for proper magneto grounding. If you flipped it from both to left or right and nothing happened, then one of the magnetos may not be properly grounded, which creates a hazard if anyone tried to turn the prop by hand.

Assuming that one knows how engines work, one can explain it this way as well: Two spark plugs that fire simultaneously provide two spark locations that are physically apart from each other where the flame from each spark need to ignite only half of the charge so to speak or in other words the flame from each spark need to travel only half the distance (roughly) to complete its portion of the charge, where burning of the total charge is accomplished earlier in the down-stroke of the piston generating more work over the total piston stoke. Hope that is understandable as well. That also explains why late ignition timing reduces power.